Elastin deposition and stenosis formation in the developing aorta

摘要 弹性蛋白是大动脉的基本组成部分，提供弹性以减少心脏工作负荷， 保护下游器官。弹性蛋白只在胚胎晚期开始的一个狭窄的时间段内表达， 在青春期结束。由于弹性蛋白70年的半衰期， 并且使得弹性蛋白在发育期的正确沉积至关重要。弹性蛋白沉积在 主要是由称为弹性层的同心层中的平滑肌细胞（SMC）。存在着复杂 升主动脉壁内存在来自不同胚胎起源和分化状态的SMC的混合物，但 这些不同的壁细胞类型如何有助于弹性层的形成是未知的。先天性突变 在弹性蛋白基因中的缺失导致弹性蛋白功能不全并引起瓣上主动脉瓣狭窄（SVAS）。没有 增加SVAS中弹性蛋白水平的治疗策略和预防性手术以减轻主动脉瓣狭窄， 避免心源性猝死的主要治疗方法。虽然手术有很好的早期效果， 需要再次手术，尤其是儿童。弹性蛋白减少导致主动脉粥样硬化的机制 狭窄还没有被很好地理解。以前的小鼠模型已经推进了我们对SVAS的理解，但新的 在发育过程中更精确地控制弹性蛋白沉积的位置和时间的小鼠模型 需要改进有争议的机制。目前提出的生物物理机制涉及以下变化： 主动脉弹性、生长、细胞增殖和/或胶原沉积至狭窄形成。的计算 主动脉生长和重塑（G&R）模型将有助于评估物理相容性， 竞争机制的局限性。计算G&R模型提供了对 成人血管疾病中的主动脉重塑，但在正常和 先天性疾病中的异常主动脉发育。本提案的总体目标是更好地了解 正常升主动脉发育中弹性蛋白沉积的过程以及弹性蛋白水平降低如何导致 主动脉发育异常导致的狭窄为实现这一目标，提出了三个具体目标：目标1。 确定主动脉壁内不同类型的细胞如何促进弹性层的形成;目的2.量化 分级弹性蛋白量对主动脉结构和心血管功能的影响;以及目的3。利用 计算模型来描述和预测弹性蛋白量和透壁组织的变化如何导致 导致主动脉瓣狭窄一种新的弹性蛋白floxed小鼠，允许弹性蛋白表达， 当培育至Cre表达系时，以细胞类型和时间点特异性方式减少的细胞数量将用于 目标1和2。基于非线性弹性、连续介质力学和应力-应变定律的计算模型， 介导的生长和基质沉积将用于目标3。目标3中的模型预测将与 目的1和2中正常和异常主动脉发育的实验结果。成功完成 这些目标可能导致治疗SVAS中弹性蛋白功能不全和/或主动脉瓣狭窄的新策略。

ABSTRACT Elastin is a fundamental component of large arteries, providing elasticity to reduce cardiac workload and protect downstream organs. Elastin is expressed only during a narrow timeframe initiating in the late embryonic stage and ending in adolescence. This short expression window is possible due to elastin’s 70-year half-life and makes correct deposition of elastin in the developmental period critically important. Elastin is deposited predominantly by smooth muscle cells (SMCs) in concentric layers called elastic laminae. There is a complex mixture of SMCs from different embryonic origins and differentiation states within the ascending aortic wall, yet how these different mural cell types contribute to elastic laminae formation is unknown. Congenital mutations in the elastin gene lead to elastin insufficiency and cause supravalvular aortic stenosis (SVAS). There are no therapeutic strategies to increase elastin levels in SVAS and preventative surgery to alleviate aortic stenosis is the primary treatment to avoid sudden cardiac death. While surgery has good early results, there is a significant need for reoperation, especially in children. The mechanisms by which reduced elastin causes aortic stenosis are not well understood. Previous mouse models have advanced our understanding of SVAS, but new mouse models with more precise control of the location and timing of elastin deposition during development are needed to refine debated mechanisms. Currently proposed biophysical mechanisms relate changes in aortic elasticity, growth, cellular proliferation, and/or collagen deposition to stenosis formation. A computational model of aortic growth and remodeling (G&R) would be useful to evaluate the physical plausibility and limitations of competing mechanisms. Computational G&R models have provided insight into processes of aortic remodeling in adult vascular disease, but have seen limited application for processes of normal and abnormal aortic development in congenital disease. The overall goal of this proposal is to better understand the process of elastin deposition in normal ascending aortic development and how reduced elastin levels lead to stenosis in abnormal aortic development. Three specific aims are proposed to accomplish this goal: Aim 1. Determine how different cell types within the aortic wall contribute to elastic laminae formation; Aim 2. Quantify the effects of graded elastin amounts on aortic structure and cardiovascular function; and Aim 3. Utilize a computational model to describe and predict how variations in elastin amount and transmural organization lead to aortic stenosis through stress-mediated G&R. A new elastin-floxed mouse that allows elastin expression to be reduced in a cell type and time point specific manner when bred to Cre expressing lines will be used for Aims 1 and 2. A computational model based on laws of nonlinear elasticity, continuum mechanics, and stress- mediated growth and matrix deposition will be used for Aim 3. Model predictions in Aim 3 will be compared to experimental results for normal and abnormal aortic development in Aims 1 and 2. Successful completion of these aims may lead to novel strategies to treat elastin insufficiency and/or aortic stenosis in SVAS.